Helper methods to propagate trace headers

[danielgerlag]

Add helper methods to propagate trace headers from an incoming invoke request or pub sub message to an outgoing invocation or pub sub message.

[danielgerlag]

In order to make my scenario work, I had to create an alternative implementation of the pubsub client that allows the trace headers to be set.

[XavierGeerinck]

Hi @danielgerlag ! Thank you for opening a ticket, seeing that you created an alternative implementation, would you have some time to share what you did? Maybe through a PR?

[DarqueWarrior]

Would this be as easy as having an optional headers parameter for all the clients? That could then be passed to the base class execute method. There is already code in HTTPClient.ts to read the headers if they are provided.